1. Field of the Invention
This invention relates to the addition of hydrogen and carbon monoxide to internal olefins to obtain substantial amounts of linear aldehydes.
2. Description of the Prior Art
Aldehydes, particularly linear aldehydes, are extremely useful as intermediates in organic synthesis because of their terminal carbonyl group which is among the most active groupings in organic compounds. For instance, they are easily reduced and oxidized and take part in a number of addition reactions. More specifically, aldehydes are readily catalytically reduced to the primary alcohols, and oxidized to the corresponding carboxylic acids. They also undergo addition and/or condensation reactions with hydrogen cyanide, alcohols, nitroparaffins as well as condensations with themselves and other carbonyl-containing compounds. Further, these aldehydes condense with ammonia and its derivatives including primary amines. The latter condensation products (which are commonly known as Schiff's bases) lend themselves to applications as surfactants or detergents when solubilized by processes such as sulfation or oxyalkylation.
Generally, aldehydes as a class are produced commercially by the catalytic addition of carbon monoxide and hydrogen to olefins in a process known as hydroformylation. In contrast to the abundance of information in the literature on the hydroformylation of alpha-olefins, there is a dearth of published information on the hydroformylation of internal olefins. This is undoubtedly attributable to the differences in reactivity between the various isomeric olefins. Generally, the nearer the double bond is to the terminal position, the higher is the reactivity. Whereas it is relatively easy to achieve high aldehyde linearity (&gt;90%) in the hydroformylation of alpha-olefin, using for examples Rh/P(OPhCl).sub.3 (Pruett and Smith, U.S. Pat. No. 3,527,809 issued Sept. 8, 1970) or PtCl.sub.2 (PPh.sub.3).sub.2 /SnCl.sub.2 (Schwager and Knifton, U.S. Pat. No. 3,981,925 issued Sept. 21, 1976), the catalytic hydroformylation of internal olefins to yield exclusively or predominantly terminal aldehydes is unknown. Catalysts to convert internal olefins to linear aldehydes must perform a dual function; isomerization and then hydroformylation. Recently, Pittman and coworkers (J. Am. Chem. Soc., 99, 1986(1977) has reported the use of cobalt cluster catalysts to hydroformylate 2-pentene to give moderate aldehyde linearity. Schwager and Knifton (U.S. Pat. No. 3,981,925 issued Sept. 21, 1976 and U.S. Pat. No. 3,996,293 issued Dec. 7, 1976) report the conversion of 2-heptane to aldehydes in low yield and low linearity using as a catalyst a ligand stabilized platinum (II) dehalide complexed with Group IVA metal halides.